Women who fear childbirth just got something else to worry about: a recent Norwegian study found that women who were scared of giving birth ended up spending more time in labor, about 8 hours versus 6.5 for women who weren’t afraid.

According to the study’s authors, 5% to 20% of pregnant women fear giving birth. The reasons vary, from the mothers being young or never having given birth before to their having pre-existing psychological problems, a lack social support or a history of abuse or bad obstetric experiences.

The study also found that mothers who feared childbirth were also more likely than unafraid women to need an emergency C-section (11% versus 7%) or assistance with instruments such as forceps for vaginal delivery (17.0% versus 11%). Overall, about a quarter of women who feared childbirth delivered without any obstetric interventions, compared with nearly 45% of women who were not afraid.

“Fear of childbirth seems to be an increasingly important issue in obstetric care. Our finding of longer duration of labor in women who fear childbirth is a new piece in the puzzle within this intersection between psychology and obstetrics,” study author Samantha Salvesen Adams of Akershus University Hospital at the University of Oslo in Norway said in a statement.

The researchers studied 2,206 women from pregnancy through childbirth. When the women were 32 weeks pregnant, the researchers assessed their fear of childbirth using a standard questionnaire. Women who scored higher than 85 were considered fearful; out of all the women, 165, or 7.5%, scored higher than 85.

The researchers then analyzed the time they spent in childbirth. Women who were afraid labored for an hour and 32 minutes longer than did other moms. Even after adjusting for other factors that affect labor, such as epidural anesthesia, induction and instrument-assisted delivery, fearful women took 47 minutes longer to deliver than women who had less apprehension about giving birth.

The authors note, however, that despite their fear, 89% scared mothers still succeeded in delivering vaginally, as they’d intended. That proportion was close to the 93% of women without fear who also succeeded.

“Generally, longer labor duration increases the risk of instrumental vaginal delivery and emergency caesarean section,” said Adams. “However, it is important to note that a large proportion of women with a fear of childbirth successfully had a vaginal delivery.”

Adams suggests that elective C-section shouldn’t be routinely recommended for fearful women, since, as the study’s findings show, they can still deliver vaginally if they wish.

The authors offer two theories for why women who are afraid of labor spend more time doing it. One is that they may psych themselves out. “Mental stress is associated with physiological arousal and release of stress hormones. During labor, high levels of stress hormones may weaken uterine contractility and thereby prolong labor in women with fear of childbirth,” says Adams.

Another explanation is that fear of childbirth may interfere with clear communication between the mother in labor and the obstetric staff. “Poor communication with health personnel may delay obstetric interventions,” Adams says.

“There are a number of reasons why women may develop a fear of childbirth,” said John Thorp, editor-in-chief of BJOG: An International Journal of Obstetrics and Gynaecology, the journal in which the new study is published, in a statement. “This research shows that women with fear of childbirth are more likely to need obstetric intervention and this needs to be explored further so that obstetricians and midwives can provide the appropriate support and advice.”